Shifters

CMOS VLSI DESIGN.. by Neil H.E. Weste,David Harris,PEARSON EDUCATION

1. 4/2/2013 DEEPESH 1 BANSAL COLLEGE OF ENGG. MANDIDEEP SHIFTERS PRESENTED BY: PRESENTED TO: ATUL VERMA(EC25) MRS. RAVITESH MISHRA BHARTI RAJPUT(EC29) DEEPESH SHUKLA(EC32) A.P. BCE, MANDIDEEP PARUL CHOUDHARY(EC63) SANDESH GOHATIYA(EC88 )

2. 4/2/2013 DEEPESH 2 PRESENTATION CONTENT Introduction of shifters Types of shifters Logical shifter Arithmetic shifter Barrel shifter Funnel shifter Types of funnel shifters

3. 4/2/2013 DEEPESH 3 INTRODUCTION OF SHIFTER Shifters are important element in many microprocessor design for arithmetic shifting, logical shifting, and rotation (Barrel shifter) functions.

4. 4/2/2013 DEEPESH 4 TYPES OF SHIFTER There are several commonly used shifters- Logical shifter Arithmetic shifter Barrel shifter(rotator) Funnel shifter

5. 4/2/2013 ATUL 5 LOGICAL SHIFTER It shift the number to the left or right and fills empty spots with 0’s. E xample- Logic Shift Right 2 110110 → _ _1101 → 001101 Example- Logic Shift Left 2 110110 → 0110_ _ → 011000

6. 4/2/2013 ATUL 6 ARITHMETIC SHIFTER Same as logical shifter, but on right shift fills the most significant bits with copies of the sign bit (to properly sign, extend 2’s complement numbers when using right shift by k for division by 2^k). Example- Arithmetic Shift Right 2 110110 → _ _1101 → 111101 For Left shift, same as Logic Shifter.

7. 4/2/2013 ATUL 7 BARREL SHIFTER Barrel shifter is a very important part of a combinational logic block. It have the ability to shift data work in a single operation over standard shift left or right registers that utilize more than one clock cycle. Rotates numbers in a cycle such that empty spots are filled with bits shifted off the other end.

8. Example- Barrel Shift Right 2 110110 → _ _1101 → 101101 Example- Barrel Shift Left 2 110110 → 0110_ _ → 011011 4/2/2013 ATUL 8

9. 4/2/2013 SANDESH 9 FUNNEL SHIFTER The funnel shifter perform all there such operations. Logic Shift Right Logic Shift Left Arithmetic Shift Right Arithmetic Shift Left Barrel Shift Right Barrel Shift Left.

10. 4/2/2013 SANDESH 10 FUNCTION OF DESIGN B is filled with bits based on original number is C what kind of shifter we want. Output is Y.

11. 4/2/2013 SANDESH 11 TABLE – FUNNEL SHIFTER Table lists what inputs should be applied to perform a left or right shift of an n-bit word A by k bits. Generating the offset for left shifts requires a 2’s complement subtraction.

12. 4/2/2013 SANDESH 12 TABLE- funnel shifter operation What kind of shifter is determined by input Z. Right or left is determined by offset.

13. 4/2/2013 SANDESH 13 TYPES OF FUNNEL SHITER There are two different types of funnel shifters. Array funnel shifter Multilevel funnel shifter

14. 4/2/2013 PARUL 14 ARRAY FUNNEL SHIFTER The simplest funnel shifter design consist o an array of n- input multiplexers accepting 1 of n-hot select signals (one multiplexer for each output bit ). Such an array shifter is shown in figure using n- mos pass transistor for a 4 bit shifter. The shift amount is conditionally inverted and allocated into select signals that are fed vertically across the array. The outputs are taken horizontally. Each row of transistors attached to an output forms on e of the multiplexers.

15. Inverters and decoders Y3 Y2 Y1 Y0 Left K[1:0] S3 S2 S1 S0 Z6 Z5 Z4 Z3 Z2 Z1 Z0 ARRAY FUNNEL SHIFTER 4/2/2013 PARUL 15

16. The array funnel shifter works reasonably well for medium sized shifters in transistor level design, but has high parasitic capacitance in larger shifters and is not amenable to standard cell designs. 4/2/2013 PARUL 16

17. MULTILEVEL FUNNEL SHIFTER K1 K0 determines offset 4/2/2013 BHARTI 17

18. Fig. shows a 4 bit shifter based on multiple levels of smaller multiplexers (which of course, can be transmission gates). In general, the first level shift +n/2 the second by n/4, and so fourth until the find level shift with such a structure, no decoder is necessary. The XOR gates on the control inputs conditionally invert the shifts. 4/2/2013 BHARTI 18

19. THANKYOU 4/2/2013 BHARTI 19